1. Field of the Invention
The present invention relates to communications systems, and more particularly, to automatic gain control in communications systems.
2. Description of the Related Art
In a typical communications system, receiver circuitry introduces noise into a received signal. For example, thermal noise, shot noise, blackbody noise, flicker noise, and other unwanted signal sources contribute to the noise floor of the receiver. If a receiver receives a small signal (i.e., a signal that has levels in a range close to the noise floor of the receiver), the received signal that is processed by the system will have a low signal-to-noise ratio, which results in unreliable data recovery and low performance (e.g., low bit error rate) of the communications system. If the receiver receives a large signal (i.e., a signal that has levels in a range close to the maximum level of the dynamic range of the receiver), saturation and/or clipping distortion may occur and result in unreliable data recovery and low performance of the communications system. Accordingly, typical receivers apply gain to the received signal prior to processing the received signal. In addition, individual receiver modules may introduce noise or distortion into the received signal during processing of the received signal. If the noise level increases without corresponding increases to the signal level, the signal-to-noise ratio of the signal decreases, which decreases performance of the receiver. Techniques for maintaining a particular signal-to-noise ratio in a receiver include applying gain to the received signal at one or more locations in the received signal path to maintain, at a target level, the voltage level of a received signal with respect to the dynamic range of the receiver modules to thereby facilitate achieving a target system performance.